Generally, a computer uses a single one hard disk as a recoding and storage medium for normal storage data. With the increment of data in the computer, a plurality of hard disks are installed to a computer as a hard disk array.
Currently, a plurality of hard disk arrays are disclosed, such as RAID0, RAID1 to RAID5, RAID0+1, etc. RAID represents redundant array of independent disks. In these structures, the contents distributed in the prior art hard disks are integrated so as to have the advantages in data accessing and management. For example, for RAID0, one set of data is divided into a plurality of data stripes which are written to different areas of the disk. If it is desired to read data from the hard disk, the data can be read out in parallel and then are integrated as the original data. Since the data is processed in parallel, the processing speed is increased, but if the data is destroyed, it is possible that the whole hard disk array can not be read.
For RAID1, the data to be stored is mirrored to another one hard disk at the same time so that a backup copy is prepared. The defect is that the speed is identical to a non-RAID structure.
In RAID 10/01, the structures of the RAID0 and RAID1 are integrated. In that the data are mirrored to another copy and then are divided into a plurality of stripes. It has the advantages of increasing read/write speed and having a backup copy, but the cost is high because four disks are necessary. Moreover, only 50% capacity is used.
Moreover, in RAID5, other than storing data in different area of the hard disk, a parity check is used so as to have the function of increasing R/W speed, and the data can be checked in read and write operation, even the destroyed data can be restored, but in this structure, the cost is high.
Referring to FIGS. 1 and 1A, a prior art hard disk structure is disclosed. In that a single hard disk 10 has a machine casing 11 with a driving unit 12 therein for driving a disk 13 to rotate within the machine casing 11. A R/W module 14 includes a R/W head 15 and a rotatable arm set 17 which is driven by a dynamic unit 16. A power port 18 and a signal I/O port 19 are installed at an outer side of the machine casing 1. In one working period, only one R/W head reads date selectively in the disk 13. Thus it is a non-RAID structure and data can not be backup. If RAID structure is used, as the RAID0 or RAID1 are used, at least two hard disks are necessary. In RAID10/01 structure, four hard disks are necessary. In RAID5 structure, at least three hard disks are necessary. Other than space of the machine casing is wasted, the wires are intricately arranged disorderly, as illustrated in FIGS. 1B and 1C.